Refractories are materials having properties that make them suitable for use as heat-resistant barriers in high temperature applications. Unshaped refractory materials have the ability to form a joint-less lining, and are often referred to as monolithic. These materials are useful for example as lining for cupolas hearth and siphon, blast furnaces, main, secondary and tilting runners, and more generally vessels or vessel spouts, ladles, tundishes, reaction chambers and troughs that contain, direct the flow or are suitable to facilitate the industrial treatment of liquid metals and slags, or any other high temperature liquids, solids or gases. Unshaped refractories are typically manufactured in powdered form and mixed with water prior to application. The wet material may be applied as a lining using techniques such as casting, spraying and gunning followed by setting and drying, prior to firing.
An important aspect of any refractory material is its ability to be dried out safely and quickly after setting. As such, the wet material should have a high permeability to gas and especially water vapour during dry-out on heating. Typically, therefore, some refractory materials, in particular those dedicated to thick and high thermal conductive linings (as for example carbon and/or SiC containing monolithics) or applications that call for very fast lining commissioning or installation in hot (i.e., 100-800° C.) conditions, are prepared using components which evolve inflammable hydrogen gas during wetting and setting which produces pores, voids and micro-cracking, which in turn increases permeability to gas, and thus enables quick water dry-out during heating. Typically, refractories are prepared including reactive metallic components which hydrolyse in the presence of water and under specific pH to yield hydrogen gas.
However, the emission of hydrogen gas is a safety concern since there is a risk of accidental explosion of emitted hydrogen during setting when mixed with oxygen from air in the presence of an ignition source. It would therefore be desirable to be able to prepare refractory materials which do not evolve hydrogen on setting.
However, owing to the absence of hydrogen and the expected concomitant decrease in permeability to gas, there is a risk that any improvement in safety could be off-set by a reduction in the capability of the refractory lining to be dried out and heated up to service temperature in a short time, or a detrimental effect on the ability to install the refractory under hot conditions on hot substrates. For example, with a reduction in pores and voids through which water vapour would escape during dry-out, there is an increased risk of explosion resulting from water vapour pressure generation inside the lining during dry-out.
There is therefore a need for further castable refractory materials which do not emit significant amounts of hydrogen on setting and which have chemical, physical, mineralogical, thermal, commissioning and/or installation properties at least as good, or even improved compared to, conventional hydrogen emitting refractory materials. For example, commissioning should be easy and rapid, and installation should be as straight forward as possible and not call for increased complexity such as requiring the use of special liquids as colloidal suspensions, or other chemicals, such as phosphoric acids, phosphate solutions, sodium silicate and organic compounds suitable for polymerization, for wet mixing.